1, 3, 5-ethylxylene recovery



United States Patent Ofiliee 2,803,687 Patented Aug.. 20, 19571,3,5-ETHYLXYLENE RECOVERY David A. McCaulay, Chicago, Ill., and ArthurP. Lien, Highland, Ind., assignors to Standard Oil Company, Chicago,111., a corporation of Indiana No Drawing. Original application August26, 1954, Serial No. 452,445. Divided and this application February 7,1956, Serial No. 563,860

2 Claims. (Cl. 260674) This invention relates to the recovery of1,3,5-ethylxylene from admixture with diethylbenzene.

This application is a division of our copending application Serial No.452,445, filed August 26, 1954.

A demand exists for styrene-type resins which have softening pointsabove that of polystyrene and also crosslinking polystyrene-type resins.Triethylbenzene and diethyltoluene are suitable sources of these typesof materials if the isomers charged to the dehydrogenation processcontain no ortho positioned groups. Essentially pure, i. e., within theerror of infrared spectrometry, which is about 2%, 1,3,5-triethylbenzeneand 1,3,5-diethyltoluene are excellent starting materials for theproduction of high softening point resins having cross-linkages.

1,3,5-ethylxylene (1ethyl-3,S-dimethylbenzene) is of interest in theproduction of high melting point styrenetype resins. Essentially purematerial is necessary since the presence of any of the other isomers ofethylxylene results in a marked decrease in the softening pointobtainable.

The process permits the separation of the close boiling mixture ofisomers of diethylbenzene and ethylxylene. These isomers boil so closetogether that they are not separable by even superfractionaldistillation. However, 1,3,5-triethylbenzene is very easily separated bydistillation from 1,3,5-ethylxylene. In the HF--BF3 treating of amixture of xylene and ethylbenzene to separate metaxylene away from theortho and para-xylenes, there is produced a C aromatic hydrocarbonfraction consisting essentially of 1,3-diethylbenzene and1,3,5-ethylxylene. By utilizing 1 mole of ethylene per mole ofdiethylbenzene in the mixture of diethylbenzene and ethylxylene, it ispossible to convert the diethylbenzene to triethylbenzene almostcompletely, thereby permitting the distillative recovery of a C10aromatic fraction containing 95% or more of 1,3,5-ethy1xylene. By usinga slight excess of not more than 1.1 moles in all of ethylene per moleof diethylbenzene, it is possible to remove the diethylbenzene socompletely that 1,3,5-ethylxylene of 99|% purity is separable bydistillation from the reaction product mixture. The reaction productmixture will contain, in addition to the triethylbenzene, sometetraethylbenzene and diethylxylene. Therefore, the amount of ethylenecharged should be controlled to attain the desired purity withoutwastage of ethylxylene.

The olefin used in the process is ethylene. Although inert diluent gasesmay be present, it is preferred to operate with commercial purityethylene or pure ethylene. The process is carried out in the presence ofliquid HF and BFs. In order to avoid hydrate formation and reducecorrosion, the process is carried out under substantially anhydrousconditions. The liquid hydrogen fluoride should not contain more thanabout 3% of water. Commercial grade anhydrous hydrofluoric acid issuitable for use in the process.

Enough liquid HF must be present in the alkylation zone to participatein the formation of an HF and BFs complex with the polyalkylbenzenecharged. It is beamount, it is necessary to have suflicient liquid HF todissolve the complex formed. In general, enough liquid HF must bepresent to form a distinct separate acid phase. More than this amount isdesirable and usually at least about 3 moles of liquid HF are used permole of aromatic hydrocarbon in the feed. More than this amount may beused, for example moles or more. It is preferred to operate with betweenabout 6 and about 12 moles of liquid HF per mole of aromatic hydrocarbonin the feed.

The temperature and the time are related in this process. In order toobtain the maximum yield of 1,3,5-triethylbenzene, it is not onlynecessary to operate for a defined time at each particular temperatureof operation,

but it is necessary to control the rate of ethylene addition. mined bycracking reactions and tar formation; this maximum temperature is about175 C. In order to avoid these undesired side reactions, the practicaltemperatureof operation is about 135 C. At these high temperatures, thenecessary time is quite short and may be on the order of 1 to 2 minutes.The process is operable at quite low temperatures provided thata'sufficiently long time is utilized. Thus, at 0 C. it may be necessaryto maintain the contents of the alkylation zone for several weeks inorder to obtain the maximum conversion to the 1,3,5-triethylbenzene. Thetime and temperature relationship is illustrated as follows: At 20 C.,the necessary time is about 3 days, i. e., 70 to 80 hours; C.--about 30minutes; 80 C.--about 10 minutes. It is to be understood that attemperatures below about 100 C. the process may be carried on for timeslonger than thoseset out above without significant harmful eifects, butalso without any appreciable beneficial effects. It is preferred tooperate at a temperature between about 50 C. and about 80 C. for a timebetween about 10 minutes and 2 hours, the longer times corresponding tothe lower temperatures.

The process involves not only addition of the ethylene to the aromatichydrocarbon, but also it is believed isomerization of the originalalkylate to the 1,3,5-configuration which appears to be the most stableconfiguration in the presence of HF-BF3 agent. In order to attain atriethylbenzene which is essentially pure 1,3,5-

triethylbenzene, it is necessary to add the ethylene to the alkylationzone at a substantially constant rate over the time needed,corresponding to the particular temperature. Put in another way, theethylene is added at about a uniform rate over the particular time. Itis preferred to add the ethylene in such a way that all of the ethylenewill have been added shortly before the end of the time corresponding tothe particular temperature. This addition is at a constant amount perunit time.

.Thefalkylate product contains triethylbenzene. alkylate produced in theethylation reaction, which triethylbenzene alkylate is essentially pure1,3,5-isomer. The term essentially pure is used herein as within theaccuracy of infrared spectrometry which is about 2% absolute. It isbelieved that operating under the described conditions, thetriethylbenzene alkylate is 99+% 1,3,5- isomer.

The results obtainable with the process of the invention are set out inExample I below. For purposes of comparison, Example II is set outshowing the alkylation of 1,3,5-ethylxylene in the absence ofdiethylbenzene.

The examples were carried out using a reactor provided with a stirrer.The hydrocarbon feed was added to the reactor followed by the additionof commercial grade anhydrous hydrofluoric acid containing about 1% ofwater. The BFs was then pressured into the reactor;

The maximum temperature of operation is deter- 1,3,5-isomer.

commercial grade cylinder BF3 was used. Commercial grade cylinderethylene was introduced into the reactor at a uniform rate over thetotal time of contacting carried on in the reactor. After all theethylene had been added, the agitation was continued for a moment or twoand then the contents of the reactor were withdrawn into a vessel filledwith crushed ice. The upper hydrocarbon layer was decanted from thelower aqueous layer which formed in the vessel. After having beenneutralized and washed, the hydrocarbons recovered were fractionated ina column providing about 30 theoretical plates. The close boilingproduct fractions from this column were analyzed by a combination ofboiling point, specific gravity, refractive index, and ultraviolet andinfrared spectrometry.

EXAMPLE I .In this example, Eastman diethylbenzene, consisting of amixture of the meta and para isomers, was charged to the reactor alongwith 1,3,5-ethylxylene. Infrared analysis indicated that thisethylxylene Was 99% -lthe Equimolar amounts of diethylbenzene andethylxylene, namely 0.64 mole, respectively, was charged. Approximately9 moles of liquid HF were charged followed by 1.52 moles of BFa. Thematerial in the reactor was agitated while 0.64 mole of ethylene wasadded over a 30 minute period. The temperature of the materials in thereactor during this time was about 30 C. The hydrocarbons recovered fromthe quenching with crushed ice represented 94% of those charged.

The product distribution set out in the table shows that within theerror of the procedure, all of the 1,3,5- ethylxylene charged wasrecovered without change from the total hydrocarbon product. A smallamount of ethylbenzene was recovered as well as some material higherboiling than triethylbenzene. This material appears to be a mixture oftetraethylbenzene and pentaethylbenzene. Within the error of infraredspectrometry, the ethylxylene recovered from the product hydrocarbonscontained only the 1,3,5-isomer and the triethylbenzene recovered fromthe product hydrocarbons contained only the 1,3,5-isomer.

EXAMPLE II In this test, 1,3,5-ethylxylene of the same composition asthat charged to Example I was introduced into the reactor in an amountof 0.5 mole. Four moles of liquid HF and 0.50 mole of BFa were thenintroduced into the reactor. The contents of the reactor were stirredwhile 0.50 mole of ethylene was added over a period of 'minutes. Thetemperature of the reactor contents during this time was 25 C.

Analysis of the total hydrocarbon product recovered showed that about 60mole percent of the 1,3,5-ethylxylene had been ethylated todiethylxylene, triethylxylene and tetraethylxylene. This is in strikingcontrast with the results in Example I wherein the diethylbenzene wasprecisely ethylated away from the 1,3,5-ethylxylene without measurablelosses of 1,3,5-ethylxylene to higher polyethylxylenes.

The detailed breakdown of the conditions of the two examples and theproduct distribution are set out in the annexed table which forms a partof this specification.

Table Example I 11 Percent Percent eed:

Diethylbenzene I Triethylxylene... Tetraethylxylene Mixture of meta andpara isomers. Pure 1,3,5-is0mer (infrared).

Thus having described the invention what is claimed is:

1. A separation process which comprises (1) under substantiallyanhydrous conditions adding ethylene to a feed consisting essentially ofdiethylbenzene and 1,3,5- ethylxylene, in a mol ratio of ethylene todiethylbenzene of between 1 and 1.1, in the presence of liquid HP, in anamount of between about 3 and 50 moles, and BFa in an amount of at least1 mole, respectively, per mole of feed, at a temperature between about20 C. and 175 C. for a time between about 2 minutes and 3 days, thelonger times corresponding to the lower temperatures, said ethylenebeing added about uniformly over said time, (2) removing HF and BFa froma hydrocarbon reaction product mixture, and (3) distillatively obtainingfrom said mixture a C10 aromatic hydrocarbon fraction consistingessentially of 1,3,5-ethylxylene.

2. A separation process which comprises 1) under substantially anhydrousconditions adding ethylene to a feed consisting essentially ofdiethylbenzene and 1,3,5- ethylxylene, in a mol ratio of ethylene todiethylbenzene of between 1 and 1.1, in the presence of liquid HF, in anamount of between about 6 and 12 moles, and BFa in an amount of at least1 mole, respectively, per mole of feed, at a temperature between about50 C. and C. for a time between about 10 minutes and 2 hours, the longertimes corresponding to the lower temperatures, said ethylene being addedabout uniformly over said time, (2) removing HF and BFa from ahydrocarbon reaction product mixture, and (3) distillatively obtainingfrom said mixture a C10 aromatic hydrocarbon fraction consistingessentially of 1,3,5-ethylxylene.

No references cited.

1. A SEPARATION PROCESS WHICH COMPRISES (1) UNDER SUBSTANTIALLYANHYDROUS CONDITIONS ADDING ETHYLENE TO A FEED CONSISTING ESSENTIALLY OFDIETHYLBENZENE AND 1,3,5ETHYLXYLENE, IN A MOL RATIO OF ETHYLENE TODIETHYLBENZENE OF BETWEEN 1 AND 1.1, IN THE PRESENCE OF LIQUID HF, IN ANAMOUNT OF BETWEEN ABOUT 3 AND 50 MOLES, AND BF3 IN AN AMOUNT OF AT LEAST1 MOLE, RESPECTIVELY, PER MOLE OF FEED, AT A TEMPERATURE BETWEEN ABOUT20* C. AND 175* C. FOR A TIME BETWEEN ABOUT 2 MINUTES AND 3 DAYS, THELONGER TIMES CORRESPONDING TO THE LOWER TEMPERATURES, SAID ETHYLENEBEING ADDED ABOUT UNIFORMLY OVER SAID TIME, (2) REMOVING HF AND BF3 FROMA HYDROCARBON REACTION PRODUCT MIXTURE, AND (3) DISTILLATIVELY OBTAININGFROM SAID MIXTURE A C10 AROMATIC HYDROCARBON FRACTION CONSISTINGESSENTIALLY OF 1,3,5-ETHYLXYLENE.